In the past, most computer servers have been designed for either single-phase AC (smaller servers) or 3-phase AC (larger servers) power configurations. Mid-range servers have had to choose between these two power supply configurations, and have had to provide power distribution units (PDUs) to convert server to the other power supply configuration. These PDUs create extra complexity, cost, and size to the server system. They require space within the server rack in addition to that of the server itself.
Single phase power configurations typically require more power cables than 3-phase or dual redundant grid power configurations. Also, as power density within servers increases, server form factors tend to migrate from the single-phase configuration to the 3-phase configuration. Customers who have used exclusively single-phase power configurations may be reluctant to convert to using 3-phase power configurations.